1. Field of the Invention
The present invention relates to an image coded data re-encoding apparatus for producing a second image coded data by applying digital signal processing to a first image coded data which is obtained by coding a digital input image signal.
2. Description of Related Art
FIG. 16 is a block diagram showing a conventional image coded data re-encoding apparatus disclosed in Japanese patent application laid-open No. 2-179186/1990, for example. It is an example of a multiple site video conference system. In this figure, the reference numeral 1 designates a master station, 2 designates a relay station, 3 designates a slave station, 10 designates an image coder of the stations, and 20 designates an image decoder. The reference numerals 101 designates an input image, 102 designates image coded data, 103 designates a decoded image signal, 104 designates image re-encoded data, and 105 designates a decoded image signal.
The operation will now be described.
The image coder 10 of the master station 1 performs coding of the input image 101, and sends the image coded data 102 to the relay station 2. The relay station 2 receives the image coded data 102 with its image decoder 20 to decode it, and generates the image re-encoded data 104 by re-encoding the decoded image signal 103 with the image coder 10. The image re-encoded data 104 thus generated by the re-encoding is transmitted to the slave station 3. The slave station 3 decodes with the image decoder 20 the image re-encoded data 104 which is relayed through the relay station 2, and uses it as the decoded image signal 105.
When holding a conference using the relay station 2 with such a decoding and relaying function, it often occurs that the master station 1 and the slave station 3 employ different coding systems. In this case, it becomes necessary to change the amount of coded data to be generated and various types of parameters such as image size and a frame rate. Thus, the relay station 2 once decodes the received image coded data 102 into the decoded image signal 103, and then re-encodes it into the image re-encoded data 104, thereby matching the different coding systems.
In this way, the conventional image coded data re-encoding apparatus has a process through which the image coded data is once decoded to be re-encoded to achieve relaying or copying of the image coded data.
Since the conventional image coded data re-encoding apparatus with such an arrangement once decodes the image coded data 102 into the decoded image signal 103, and then re-encodes the decoded image signal 103 regardless of its contents to relay or convert the image coded data 102, it has some problems such as degrading the image quality of the decoded image signal 105, increasing a delay involved in the relay and transform, and augmenting the size of the apparatus.